EP0218530B1 - Ionic concentration measurement method - Google Patents

Ionic concentration measurement method Download PDF

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Publication number
EP0218530B1
EP0218530B1 EP86402169A EP86402169A EP0218530B1 EP 0218530 B1 EP0218530 B1 EP 0218530B1 EP 86402169 A EP86402169 A EP 86402169A EP 86402169 A EP86402169 A EP 86402169A EP 0218530 B1 EP0218530 B1 EP 0218530B1
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EP
European Patent Office
Prior art keywords
ion
electrode
electrochemical
ionic concentration
sensor
Prior art date
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EP86402169A
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German (de)
English (en)
French (fr)
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EP0218530A2 (en
EP0218530A3 (en
Inventor
Shuichiro Yamaguchi
Norihiko Ushizawa
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Terumo Corp
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Terumo Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/42—Measuring deposition or liberation of materials from an electrolyte; Coulometry, i.e. measuring coulomb-equivalent of material in an electrolyte
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/403—Cells and electrode assemblies
    • G01N27/4035—Combination of a single ion-sensing electrode and a single reference electrode
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/28—Electrolytic cell components
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
    • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
    • G01N27/416—Systems
    • G01N27/49—Systems involving the determination of the current at a single specific value, or small range of values, of applied voltage for producing selective measurement of one or more particular ionic species

Definitions

  • This invention relates to a novel method of measuring ionic concentration. More particularly, the invention relates to a method of measuring ionic concentration by amperometry using an electrochemical ion sensor.
  • the measurement of ionic concentration in the prior art entails utilizing a potentiometric method, according to which ionic concentration is determined by measuring equilibrium potential. Since equilibrium potential varies with the logarithm of ionic concentration, an advantageous feature of the potentiometric method is that even low concentrations can be measured with good precision.
  • a small size ion-sensor comprising an ion-sensitive film formed by electrolytic oxidation polymerization of a hydroxy or nitrogenous aromatic compound on the surface of a conductive base body and a film consisting of a plasma-polymerized organic monomer on the surface of the ion-sensitive film is disclosed in JP-A-59,142,451.
  • the inventor has conducted a variety of researches and has perfected the present invention upon discovering that it is possible to measure ionic concentration amperometrically if use is made of an electrode of a certain type.
  • the present invention provides a method of measuring H+ ionic concentration within a range of pH of 2-8 or Na+ ionic concentration within a range of pNa of 1-3, comprising the steps of forming an electrochemical call by immersing an electrochemical ion sensor exhibiting ion selectivity with respect to an ion of interest and a reference electrode into the solution of interest, measuring a current which flows through said electrochemical cell while the electrochemical ion sensor is held at a constant potential with respect to the reference electrode, said method being characterized by using an electrochemical ion sensor comprising an electrically conductive substrate, a redox layer deposited on a surface of said electrically conductive substrate, and an ion selective layer, which has a coefficient of selection of not more than 10 ⁇ 1 with respect to the ion of interest, deposited on a surface of said redox layer : said electrochemical ion sensor having an electrode resistance of not less than 103 ⁇ /cm2 ; and by converting the current value into ionic concentration value through
  • An electrochemical ion sensor employed in the present invention must exhibit ion selectivity to the ion of interest and must have a high electrode film resistance. Since the inventive method relies upon amperometry, using an electrochemical ion sensor that is not ion-selective to the ion of interest is undesirable because a measurement error will be produced by the influence of ions of a type other than the ion of interest, and by the influence of an electrolytic current of substances reacting with the electrode. Using an electrode film resistance that is not sufficiently high is undesirable since the current flowing through the battery will grow large in magnitude and greatly increase the amount of the ion of interest electrolyzed, thus making it impossible to measure the equilibrium concentration of the ion of interest.
  • an electrochemical ion sensor suitable for use in the present invention ordinarily has a coefficient of selection of not more than 10 ⁇ 1 with respect to ions other than the ion of interest and an electrode film resistance of not less than 103 ⁇ /cm2.
  • an electrochemical ion sensor that satisfies the above conditions is one comprising an electrically conductive substrate, a film having a reversible redox function deposited on the surface of the electrically conductive substrate, and an ion selective film deposited on the surface of the first-mentioned film.
  • the electrically conductive substrate used in the ion sensor may consist of an electrically conductive carbon material such as basal plane pyrolytic graphite (hereafter referred to as "BPG") or glassy carbon, a metal such as gold, platinum, copper, silver, palladium, nickel or iron, especially a precious metal, or a composite obtained by coating any of these metals with a semiconductor such as indium oxide or tin oxide.
  • BPG basal plane pyrolytic graphite
  • the electrically conductive carbon material is preferred, especially BPG.
  • the redox layer refers to one in which an electrode comprising an electrically conductive substrate having this layer deposited on its surface is capable of generating a constant potential on the substrate owing to a redox reaction.
  • an especially preferred redox layer is one which will not allow the potential to fluctuate due to the partial pressure of oxygen gas.
  • Particularly suitable examples of the redox layer are (1) an organic compound membrane or a polymeric membrane capable of a quinone-hydroquinone type redox reaction, and (2) an organic compound membrane or polymeric membrane capable of an amine-quinoid type redox reaction, and (3) electrically conductive material (e.q. polypyrrole and poly thionylone).
  • the quinone-hydroquinone type redox reaction is expressed by e.g. the following reaction formula, taking a polymer as an example: where R1, R2 represent e.g. compounds having a structure containing an aromatic series.
  • the amine-quinoid type redox reaction is expressed by e.g. the following reaction formula, taking a polymer as an example: where R3, R4 represent e.g. compounds having a structure containing an aromatic series.
  • examples of compounds capable of forming the layer having the redox function are those which undergo a redox reaction.
  • poly(N-methyl-aniline) [Onuki, Matsuda, Oyama, Nihon Kagakukaishi, 1801 - 1809 (1984)], poly)2,6-dimethyl-1,4-phenylene ether), poly(o-phenylenediamine), poly(phenyl) and polyxylenol
  • organic compounds containing the compounds (a) through (d) such as pyrazolonequinone group-containing vinyl compound-polymers, isoalloxazine group-containing vinyl compound-polymers and other quinone group-containing compound-polymers, lower polymeric compounds (oligomers) of compounds (a) through (d), or substances obtained by fixing the compounds of (a) through (d) to polymeric compounds such as polyvinyl compounds and polyamide compounds.
  • the term "polymer” is taken to mean both homopolymers and mutual
  • a polymer in order to deposit the compound capable of forming the redox layer on the electrically conductive substrate, a polymer is obtained by synthesizing an amino aromatic compound, a hydroxy aromatic compound or the like on an electrically conductive substrate of electrically conductive carbon or a precious metal by an electrolytic oxidation polymerization method or electro-deposition method, or a polymer synthesized by application of electron beam irradiation, light or heat, is dissolved in a solvent. The resulting solution is deposited on the electrically conductive substrate by painting or dipping.
  • electrolytic oxidation polymerization method the most preferred is electrolytic oxidation polymerization method.
  • the electrolytic oxidation polymerization method is implemented by subjecting the amino aromatic compound or hydroxy aromatic compound to electrolytic oxidation polymerization in a solvent in the presence of a suitable supporting electrolyte and depositing a layer of the polymer on the surface of the electrically conductive substrate.
  • a suitable supporting electrolyte are acetonitrile, water, dimethylformamide, dimethylsulfoxide, propylene carbonate and the like.
  • Preferred examples of the supporting electrolyte are sodium perchlorate, sulfuric acid, sodium sulfate, phosphoric acid, boracic acid, tetraofluoro-potassium phosphate, quaternary ammonium salts and the like.
  • the deposited polymeric film generally exhibits a high density and is capable of blocking permeation of oxygen even if thin.
  • the redox film should exhibit oxidation-reduction reactivity. Other than this, no particular limitation is placed upon the film, including the density thereof.
  • the membrane thickness of the redox layer is 0.01 ⁇ m - 0.5 mm, preferably 0.1 - 10 ⁇ m.
  • a membrane thickness of less than 0.01 ⁇ m does not fully bring forth the effects of the invention, while a thickness of more than 0.5 mm is undesirable from the viewpoint of miniaturizing the sensor.
  • the redox layer used in the present invention can be used in a form impregnated with an electrolyte.
  • the electrolyte are phosphoric acid, dipotassium hydrogen phosphate, sodium perchlorate, sulfuric acid, tetrafluoro borate, tetraphenyl borate and the like.
  • a simple method which can be adopted is to coat the electrically conductive substrate with the redox layer and then immerse the resulting membrane into a solution of the electrolyte.
  • a membrane a neutral carrier membrane
  • an ion carrier material selective to the ion of interest and, if necessary, an electrolytic salt are carried on a polymeric compound.
  • Examples of a hydrogen ion carrier material which were proposed before by Noboru Oyama (one of the inventors of the present invention), are amines expressed by the formula where R7, R8, R9 represent the same or different alkyl groups, among which at least two alkyl groups have a carbon number of 8 - 18 , and compounds expressed by the formula where R10 represents an alkyl group having a carbon number of 8 - 18 .
  • Tri-n-dodecylamine is especially preferred.
  • valinomycin examples of which can be mentioned are valinomycin, nonactin, monactin, crown ether compounds such as dicyclohexyl-18-crown-6, naphtho-15-crown-5, bis(15-crown-5) and the like.
  • valinomycin and bis)15-crown-5) are ideal.
  • aromatic amides or diamides examples which can be mentioned are aromatic amides or diamides, aliphatic amides or diamides, and crown compounds, e.g. bis[12-crown-4)methyl] dodecylmalonate, N,N,N,N-tetrapropyl-3,6-dioxanate diamide, N,N,N,N-tetrabenzyl-1,2-ethylenedioxy diacetoamide, N,N'-dibenzyl-N,N'-diphenyl-1,2-phenylendiacetoamide, N,N',N"-triheptyl-N,N'N"-trimethyl-4,4',4"-propylpyridine tris(3-oxythabutylamide), 3-methoxy-N,N,N,N-tetrapropyl-1,2-phenylendioxydiacetoamide, (-)-(R,R)-4,5-dimethyl-N,N,N,N
  • quaternary ammonium salts expressed by the formula where R7, R8, R9 represent the same or different alkyl groups having a carbon number of 8 - 18, and R10 represents hydrogen or an alkyl group having a carbon number of 1 - 8, and a triphenyl tin chloride expressed by the formula
  • Suitable examples are bis[di-(octylphenyl) phosphate], (-)-(R,R)-N,N'-bis[11-ethoxy carbonyl) undecyl]-N,N',4,5-tetramethyl-3,6-dioxaoctane-diamide and calcium bis[di(n-decyl) phosphate].
  • R11, R12, R13 represent the same or different alkyl groups having a carbon number of 8 - 18, R14 represents hydrogen atom or an alkyl group having a carbon number of 1 - 4, and X ⁇ represents Cl ⁇ , Br ⁇ or OH ⁇ , tertiary amine compounds expressed by the formula where R15 represents a phenyl groups, hydrogen atom or a methyl group, R16 represents hydrogen atom or a methyl group, and R17 represents a methyl group or an octadecyl group , and a compound expressed by the formula
  • electrolytic salt examples include sodium tetrakis(p-chlorophenyl) borate, potassium tetrakis(p-chlorophenyl) borate, and a compound expressed by the formula (R18)4NBF4 where R18 represents an alkyl group, preferably an alkyl group having a carbon number of 2 - 6.
  • polymer compound examples include organic polymer compounds such as vinyl chloride resin, vinyl chloride - ethylene copolymer, polyester, polyacryl amide and polyurethane, and inorganic polymer compounds such as silicone resin.
  • organic polymer compounds such as vinyl chloride resin, vinyl chloride - ethylene copolymer, polyester, polyacryl amide and polyurethane
  • inorganic polymer compounds such as silicone resin.
  • plasticizer does not readily elute.
  • plasticizer are dioctyl sebacate ester, dioctyl adipate ester, dioctyl maleate ester and di-n-octyl phenylphosphonate.
  • a preferred process is to prepare a solution by dissolving 50 - 500 parts by weight of a plasticizer, 0.1 - 50 parts by weight of an ion carrier substance and an electrolyte salt in 100 parts by weight of a polymeric compound serving as a carrier, dip the substrate electrode (the electrode coated with the redox layer) into the solution, lift the electrode from the solution and blow-dry it for 3 min at a temperature of 80°C. The dipping, lifting and drying steps are repeated 30 times. It is preferred that the ion carrier have a film thickness of 50 ⁇ m - 3 mm, particularly 0.3 - 2 mm.
  • An alternative method of obtaining an ion carrier film is to mix a vinyl chloride paste, an ion carrier substance, a plasticizer and an electrolyte salt in the proportions mentioned above, place the mixture on the substrate electrode to a thickness of 50 ⁇ m - 3 mm, an apply heating at a temperature of 150°C for 1 min to form a gel, thus providing the ion carrier film. If the ion-selective film thus deposited has a film thickness of, say, 1 mm, its resistance will be 103 - 106 ⁇ /cm2. This makes it possible to effectively prevent the influence of dissolved oxygen in the solution under examination, as well as the influence of other coexisting substances.
  • Fig. 1 shows an example of a set-up for measuring the ionic concentration of the solution of interest using the above-described electrochemical ion sensor.
  • the solution shown at numeral 22, is poured into a tank 21.
  • Numeral 23 denotes the electrochemical ion sensor, and 24 designates a reference electrode, such as a silver/silver chloride electrode or calomel electrode.
  • the ion sensor 23 and reference electrode 24 are immersed in the solution 22. Electrolysis is carried out while holding the potential of the electrochemical ion sensor 23 constant with respect to the reference electrode 24 by means of a potentiostat 25. A current that flows at this time is measured by an ammeter 26.
  • the ionic concentration of the solution is read from a previously prepared calibration curve in which current is plotted against ionic concentration.
  • a cyclic voltammogram is taken at a sufficiently low sweep rate (e.g. 2 mV/sec) when the electrochemical ion sensor used in the invention and the reference electrode are immersed in a standard solution, current-potential curves of the kind shown in Fig. 5 are obtained. In the wave forms obtained, the magnitude of the current depends essentially upon the electrode film resistance. If electrolysis is carried out under the above conditions while the potential of the electrochemical ion sensor is held constant with respect to the reference electrode in a standard solution having various ionic concentrations, then the observed current will exhibit a substantially linear relationship with respect to the logarithm of ionic concentration.
  • the observed current is proportional to the logarithm of the ionic concentration. Therefore, in accordance with the invention method, ionic concentration can be precisely measured over a wide range just as with the potentiometric method despite the fact that amperometry is employed.
  • the pH sensor illustrated in Fig. 2 was fabricated by the following method:
  • the electrolytic solution used was acetonitrile containing 0.2 M of sodium perchlorate as a supporting electrolyte and 0.5 M of 2,6-xylenol.
  • An electrolyzing potential was swept three times (sweep rate: 50 mV/sec) from 0 to 1.5 V, followed by carrying out constant-potential electrolysis for 10 min at 1.5 V.
  • An electrolytic oxidative polymeric film (thickness: about 30 ⁇ m) 13 of 2,6-xylenol was thus formed on the exposed end face of the BPG substrate.
  • the electrolytic oxidative polymeric film was dark blue in color.
  • the pH sensor obtained in Referential Example 1 and a SSCE were immersed in standard phosphate buffer solutions (pH 2,18, 4.04, 6.01, 8.11) and the potential of the pH sensor with respect to the SSCE was regulated to 0.3V.
  • the steady-state value of current was measured about 5 sec after the application of voltage.
  • the results are shown in Fig. 3, from which it is clear that the values of pH and current are linearly related within the range of pH 4 - 8, indicting that pH can be measured amperometrically.
  • a pH sensor was fabricated as in Referential Example 1, with the exception of the fact that the load of tetrahydrofuran in the dipping solution mentioned in (ii) was changed to 20 ml and the film thickness of the hydrogen ion-selective film was made 0.48 mm. Upon measuring the electrode resistance as in Referential Example 1, the resistance value was found to be 1.5 x 105 ⁇ /cm2.
  • Fig. 4 shows the cyclic voltammogram obtained through measurement with a cell of the same construction.
  • a pH sensor was fabricated as in Referential Example 1, with the exception of the fact that 1-aminopyrene was used instead of 2,6-xylenol as a monomer of the electrolytically oxidized polymeric film.
  • the electrode resistance, measured as in Referential Example 1, was found to be 8 x 104 ⁇ /cm2.
  • An electrolytic oxidative polymeric film-coated electrode was fabricated as in (i) of Referential Example 1.
  • the electrode was then dipped in a solution containing a sodium ion carrier having a composition set forth hereinbelow.
  • the electrode was then removed from the solution and dried.
  • a sodium-ion selective film was deposited on the electrolytic oxidative polymeric film.
  • These dipping and drying steps were repeated 30 times so that the sodium-ion selective film formed had a thickness of about 0.3 mm.
  • the electrode resistance, measured as in Referential Example 1, was found to be 1 x 105 ⁇ /cm2.
  • the sodium ion sensor obtained in Referential Example 4 and a SSCE were immersed in 10 ⁇ 1 - 10 ⁇ 3 M sodium chloride solutions and the potential of the sodium ion sensor with respect to the SSCE was regulated to 0.6V.
  • the steady-state value of current was measured about 10 sec after the application of voltage.
  • the results are shown in Fig. 7, from which it is clear that the values of pNa and current are linearly related within a range of pNa 1 - 3, indicating that pNa can be measured amperometrically.

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EP86402169A 1985-10-02 1986-10-02 Ionic concentration measurement method Expired - Lifetime EP0218530B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP60219882A JPS6279345A (ja) 1985-10-02 1985-10-02 イオン濃度測定方法
JP219882/85 1985-10-02

Publications (3)

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EP0218530A2 EP0218530A2 (en) 1987-04-15
EP0218530A3 EP0218530A3 (en) 1989-03-15
EP0218530B1 true EP0218530B1 (en) 1992-09-09

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EP86402169A Expired - Lifetime EP0218530B1 (en) 1985-10-02 1986-10-02 Ionic concentration measurement method

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EP (1) EP0218530B1 (enrdf_load_stackoverflow)
JP (1) JPS6279345A (enrdf_load_stackoverflow)
KR (1) KR910002090B1 (enrdf_load_stackoverflow)
DE (1) DE3686694T2 (enrdf_load_stackoverflow)
DK (1) DK468586A (enrdf_load_stackoverflow)

Families Citing this family (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4929313A (en) * 1984-11-23 1990-05-29 Massachusetts Institute Of Technology Amperometric electrochemical ion sensors and method for determining ion concentration
GB8806145D0 (en) * 1988-03-15 1988-04-13 Unilever Plc Electrical sensor & method
JPH04303713A (ja) * 1991-03-30 1992-10-27 Atlas Kk ミネラルイオン水の監視装置
FR2693894B1 (fr) * 1992-07-24 1994-09-30 Seb Sa Procédé pour modifier les caractéristiques d'une surface de métal.
KR100823117B1 (ko) * 2006-08-23 2008-04-18 부산대학교 산학협력단 이온 선택성 미소전극의 전위 측정 장치
US20140332411A1 (en) * 2011-12-23 2014-11-13 Schlumberger Technology Corporation Electrochemical sensor for ph measurement
GB2501769A (en) * 2012-05-04 2013-11-06 Schlumberger Holdings Electrochemical sensor for pH measurement

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58172541A (ja) * 1982-04-02 1983-10-11 Terumo Corp イオン電極用基体およびイオン電極
US4440603A (en) * 1982-06-17 1984-04-03 The Dow Chemical Company Apparatus and method for measuring dissolved halogens
DE3585915T2 (de) * 1984-12-28 1993-04-15 Terumo Corp Ionensensor.

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Publication number Publication date
DK468586D0 (da) 1986-10-01
DE3686694T2 (de) 1993-04-01
JPS6279345A (ja) 1987-04-11
EP0218530A2 (en) 1987-04-15
DK468586A (da) 1987-04-03
KR910002090B1 (ko) 1991-04-03
KR870004304A (ko) 1987-05-08
DE3686694D1 (de) 1992-10-15
JPH0446378B2 (enrdf_load_stackoverflow) 1992-07-29
EP0218530A3 (en) 1989-03-15

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